The purpose of a control chart is to eliminate common cause variation

Question:A factory supervisor is concerned that the time it takes workers to complete an important production task (measured in seconds) is too erratic and adversely affects expected profits. The supervisor proceeds by randomly sampling 5 individuals per hour for a period of 10 hours. The sample mean and range for each hour are listed below.

Suppose the supervisor constructs an R chart to see if the variability in collection times is in-control. The upper and lower control limits for the R chart are approximately UCL = 43.13 and LCL = 5.13 

The process is in control.